US7078276B1 - Nanoparticles and method for making the same - Google Patents

Abstract

A method for making nanoparticles, nanoparticle inks and device layers therefrom is disclosed. In accordance with the present invention, nanoparticles are isolated from a composite material that is formed by treating a metal oxide precursor to form the metal nanoparticles and a metal oxide matrix. The nanoparticles are then isolated from the composite material by etching at least a portion of the metal oxide matrix to release the metal nanoparticles. In accordance with the embodiments of the invention, the nanoparticles are treated with surfactants and wetting agents either while etching or after etching, are isolated from the etchant and dispersed in a solvent medium and/or are otherwise treated or modified for use in a nanoparticle inks. A layer of the metal nanoparticle ink can then be used to form doped, undoped, patterned and unpatterned device layers or structures in micro-devices.

Description

FIELD OF THE INVENTION

The present invention relates to micro-devices. More specifically, the present invention relates to methods of fabricating micro-devices using nanoparticles.

BACKGROUND OF THE INVENTION

Ultra-fine particles or nanoparticles (particles having an average diameter of 200 nanometers or less) are believed to be useful in the fabrication of micro-electronic devices. Alivisatos et al., in U.S. Pat. No. 5,262,357, describe a method for making semi-conductor nanoparticles from semi-conductor precursors. Alivisatos et al. describe using these semi-conductor nanoparticles to make continuous semi-conductor films. Because the semiconductor nanoparticles exhibit significantly lower melting temperature than bulk materials, a layer of the semi-conductor nanoparticles can be deposited on a substrate and annealed at relatively low temperatures, whereby the nanoparticles melt to form a continuous film.

One of the goals for nano-technology is to develop techniques and materials that will allow for the fabrication of micro devices on a variety of substrates using selective deposition, printing and/or imaging technologies. These selective deposition, printing and/or imaging technologies can utilize nanoparticies, or inks comprising nanoparticles, to fabricate device layers and structures in micro-devices.

There have been recent efforts to make metal-based solutions which can be used to make conductive device layers in the fabrication of micro-electronic devices. For example, Kydd in U.S. Pat. No. 5,882,722 describes a method of forming conductive layers from a suspension of mixtures of a metal powder and an organo-metallic compound dispensed in an organic solvent. The suspension is deposited onto a substrate to form a layer. The layer of the suspension is then cured to remove solvents and surfactants and decomposed the mixture of the metal powder and the organo-metallic compound to form the conductive layer.

Nanoparticle technologies provide alternative methods to laborious and expensive lithographic techniques for the fabrication of micro-devices and/or methods. Therefore, there is a continued need to develop new methods for making nanoparticles and new methods for using the nanoparticles in the fabrication of micro-devices that can reduce the number of mask and etch steps required during the fabrication of the micro-devices.

SUMMARY OF THE INVENTION

The present invention is directed to methods for making nanoparticles and uses thereof. The nanoparticles of the present invention preferably have average diameter of 200 nanometers or less and preferably 100 nanometers or less. In accordance with the embodiments of the invention, the nanoparticles are metal nanoparticles that are isolated from a composite material comprising the metal nanoparticles. It is understood that metal nanoparticles herein refers to nanoparticles comprising transition metal elements and/or semiconductor elements, such as silicon and germanium.

The composite material is preferably formed by treating a metal oxide precursor to conditions, such as elevated temperatures, which causes the metal oxide precursor to disproportionate and form the metal nanoparticles and an oxide matrix, wherein the oxide matrix comprises higher metal oxides. Metal oxide precursors, suitable for making metal nanoparticles include, but are not limited to, oxides of cobalt, vanadium, manganese, niobium, iron, nickel, copper, silicon, titanium, germanium, zirconium, tin and combinations thereof. In accordance with a preferred embodiment of the invention, one or more of the metal oxide precursors that are used to form the metal nanoparticles are metal monoxide precursors, such as a silicon monoxide precursor. After the composite material is formed, the metal nanoparticles are isolated from the composite material. The metal nanoparticles are preferably isolated from the composite material using an etchant medium to release the metal nanoparticles from the oxide matrix. In accordance with the embodiments of the invention, the etchant medium comprises a hydrogen fluoride source, which is an inorganic hydrogen fluoride source (such as NH₄F, HF, KHF₂and KF or a combination thereof). In further embodiments of the invention, the hydrogen fluoride source is an organo-ammonium fluoride (such as pyridine:HF or any other secondary or tertiary amine:HF material). The etchant medium, in accordance with still further embodiments of the invention, comprises a surfactant, such as an amine, an amine oxide, a quaternary ammonium salt, a betaine, a sulfobentaine, a ether, a polyglycol, a polyether, a polymer, an organic ester, an alcohol, a phosphine, a phosphate, a carboxylic acid, a carboxylate, a thiol, a sulfonic acid, a sulfonate, a sulfate, a ketone, a silicone, or a combination thereof. More specific example of surfactants include, but are not limited to, methyl laureate, methyl oleate, dimethyl succinate, propyleneglycol, diglyme, hexadecylamine, ethyl dimethyl amine oxide, tetraoctyl ammonium bromide, poly n-vinyl pyrrolidone, octanol, tributyl phosphine, tributyl phosphate, trioctyl phosphine oxide, hexadecyl thiol, dodecyclbenzene sulfonate, diisobutyl ketone and dodecylohexacyclomethicone. In yet further embodiments of the invention, an etchant medium comprises a wetting agent such as a fluorinated surfactant and/or a fluorinated hydrocarbon, either alone or in combination with one or more of the aforementioned surfactants. Specific examples of wetting agents include, but are not limited to, perfluorohexanoic acid, perflourodecane, perfluoromethylvinyl ethers and hexafluoropropylene oxides.

Nanoparticles, in accordance with the embodiments of the invention, are hydrogen capped nanoparticles or nanoparticles capped with a surfactant, such as those described above. Alternatively, surfactant capped nanoparticles can be converted to hydrogen capped nanoparticles by treating the nanoparticles to lithium aluminum hydride, boro-hydride, or any other suitable hydride source.

Nanoparticles, in accordance with present invention, are doped or undoped. To form doped metal nanoparticles, a metal oxide precursor is treated which causes the metal oxide precursor to disproportionate in the presence of a dopant source, such that a dopant element from the dopant source is incorporated into the metal nanoparticles formed. The dopant source is preferably a molecular dopant source, which includes one or more atoms of the doping element such as boron, phosphorus and arsenic. Alternatively, or in addition to, doping metal nanoparticles during disproportionation of a metal oxide, metal nanoparticles can be doped after disproportionation of a metal oxide using techniques such as ion implantation.

In accordance with further embodiments of the invention, when the etchant medium is aqueous, isolating metal nanoparticles from the composite material can further comprises interfacing the aqueous etchant medium with an organic extraction medium, in order to extract the metal nanoparticles from the aqueous etchant medium after or while the metal nanoparticles are being released from the oxide matrix. In accordance with still further embodiments of the invention, the etchant medium comprises a bistable phase medium, such as a fluorous-phase medium, wherein the etchant medium is a single phase at a first temperature and during the etching process. After the etching process, the bistable phase medium is converted to separate phases at a second temperature (that is generally lower than the first temperature), wherein the nanoparticles have a preferred affinity, or solubility, in one or more of the separated phases. Once nanoparticles of the present invention are isolated, washed, and/or treated, the nanoparticles are preferably used in the formulation of a nanoparticle ink that can then be used in the fabrication of micro-devices (i.e., micro-electronic, micro-mechanical and micro-optical devices,) and/or for micro-device systems and applications including, but not limited to, biological imaging systems and applications.

A nanoparticle ink, in accordance with the embodiments of the present invention, is formed by dispersing nanoparticles into a solvent medium which preferably comprises one or more organic solvents, but can also be an aqueous solvent medium especially where the nanoparticle ink is used for biological applications. The ink formulation used, in accordance with further embodiments of the invention, comprises one or more surfactants and/or wetting agents, such as those previously mentioned. In still further embodiments of the invention, the nanoparticle ink comprises a molecular precursor that is preferably a silicon-based molecular precursor (such as a polysilane, a silylene or an organo-silane), a germanium-based molecular precursor (such as a polygermane, a germylene or an organo-germane) or a combination thereof. The molecular precursor, in accordance with still further embodiments of the invention, comprises one or more dopant elements, such as arsenic, phosphorus and/or boron, which can incorporate into a device layer.

In accordance with the embodiments of the present invention, a device layer (i.e. a conductive layer, a dielectric layer or a semiconducting layer), is formed by depositing a nanoparticle ink comprising metal nanoparticles that are dispersed in a solvent medium onto a suitable substrate structure. The suitable substrate structure comprises any number of materials including, but not limited to silicon, metal, quartz, glass and polymer materials, (i.e., polyimide). The substrate structure can also include any number of previously fabricated device layers, such as conductive layers, dielectric layers, semiconducting layers or combinations thereof.

The nanoparticle ink is deposited onto the substrate structure using any suitable deposition technique, including but not limited to, ink-jet printing, screen printing, slide-bar coating, spin coating, extrusion coating, meniscus coating, dip coating and spray coating. The layer of ink is deposited as a patterned, or an unpatterned layer. After depositing the layer of nanoparticle ink, the layer is preferably cured such that at least a portion of solvent medium, surfactants and/or wetting agents are removed from the layer and the nanoparticles fuse together. It is believed that incorporation of the molecular precursor (such as a silicone-based molecular precursor) into the nanoparticle ink formulation, can aid the ability of the nanoparticles to fuse together and/or facilitate doping of the device layer during a curing process. When a layer of nanoparticle ink is deposited as a continuous layer, the continuous layer of nanoparticle ink, in accordance with the embodiments of the present invention, can be patterned before curing using liquid embossing techniques. A patterned layer can also be formed by selective deposition techniques, such as ink jet printing, wherein the nanoparticle ink is deposited in a pattern and is then cured. Further, a patterned layer can be formed by selective curing techniques, wherein a layer of nanoparticle ink is selectively cured in a pattern using a laser to write the pattern and/or the layer of nanoparticle ink is cured through a mask, wherein uncured regions of the layer nanoparticle ink can then be removed.

Alternatively, or in addition to patterning the layer using liquid embossing techniques, a cured layer of ink can be patterned using lithographic techniques (mask/etch processes and nano-imprint lithography), laser ablation and/or any other suitable technique for patterning a solid phase layer, including

Nanoparticle inks comprising a dopant precursor preferably result in device layers that are doped, as described previously. Alternatively, or in addition to forming doped layers via inclusion of a molecular dopant precursor, doped nanoparticles, or a combination thereof in a nanoparticle ink formulation, doped device layers can be formed using implanting techniques, after a patterned or an unpatterned layer of nanoparticle ink is deposited and cured.

In still further embodiments of the invention a nanoparticle ink, such as those described above, is used to form a seed layer on a suitable substrate structure. Accordingly, forming a device layer further comprises depositing an ink layer comprising a silicon-based or germanium-based molecular precursor and curing the layer or depositing a silicon-based or germanium-based molecular precursor over the seed layer using vapor deposition techniques.

In accordance with the embodiments of the invention, an ink comprises a bulk nanoparticle source, such as described above and a crystallization promoter. Suitable crystallization promoters include, but not limited to, organometallic compounds and/or metal nanoparticles of Ni, Au, Al and Fe. For example, semiconductor nanoparticles (as a bulk nanoparticle source) and an amount of an organometallic and/or metal nanoparticles of Ni, Au, Al and Fe (as a crystallization promoter) are dispersed or dissolved in a suitable solvent medium along with any number of surfactants and/or wetting agents. The ink is then deposited onto a suitable substrate and cured to form a semiconductor-based pattern or unpatterned device layer.

In yet further embodiments of the invention, a metal layer is used as a crystallization promoter, either alone or along with an ink comprising one or more organometallic and/or nanoparticle crystallization promoters, such as described above. In accordance with the embodiments of the invention, a substrate structure comprises a patterned or unpatterned metal layer that is deposited using vapor deposition of a molecular precursor, electroless plating, sputtering or any other suitable deposition method. A patterned or unpatterned layer of ink is deposited over meal layer and is cured to form a pattern or unpatterned device layer. The aforementioned molecular and nanoparticle crystallization promoters used in ink formulations and metal layer crystallization promoters are believed to help crystalize nanoparticles and form a device layer during a curing and/or annealing process. Metal layers suitable for promoting crystallization preferably include one or more metal of Ni, Au, Al and Fe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A–E are equations illustrating making metal nanoparticles, isolating the metal nanoparticles and formulating nanoparticle inks therefrom, in accordance with the embodiments of the present invention.

FIGS. 2A–D are flow-charts outlining the steps for making metal nanoparticles, isolating the metal nanoparticles, formulating nanoparticle inks, and fabricating device layers therefrom, in accordance with the embodiments of the present invention.

FIGS. 3A–C schematically illustrate forming a patterned device layer on a substrate structure using liquid embossing, in accordance with the embodiments of the present invention.

FIGS. 4A–B are flow-charts outlining the steps for making a seed layer on a substrate structure and the formation of a device layer thereon, in accordance with further embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, nanoparticles are isolated from acomposite material107 and can then be used to form a nanoparticle ink and form device layers therefrom, as described below. Nanoparticles are generally referred to herein as particles having average diameters of 200 nanometers or less, and preferably 100 nanometers or less.Nanoparticles103, in accordance with the embodiments of the present invention, are formed by treating ametal oxide precursor101 to conditions, such as elevated temperatures (ΔT), causing themetal oxide precursor101 to disproportionate and form themetal nanoparticles103 embedded in anoxide matrix105 in thecomposite material107.Metal oxide precursors101 is any suitable metal oxide precursor capable of undergoing a disproportionation process, such as cobalt, vanadium, manganese, niobium, iron, nickel, copper, silicon, titanium, germanium, zirconium, tin oxides and combinations thereof. Preferably, however, the metal oxide precursor is a metal monoxide and most preferably the metal oxide precursor is silicon monoxide, which forms silicon nanoparticles embedded in a matrix of silicon monoxide and silicon dioxide.

Nanoparticles103, in accordance with the present invention, are doped or un-doped. To form doped nanoparticles, a dopant source is included during the disproportionation process, as shown inFIG. 1A, wherein an amount of a doping element from the dopant source is incorporated into thenanoparticles103 formed. The dopant source is preferably a molecular dopant source which includes one or more atoms of the doping element, such as boron, phosphorus and arsenic. Accordingly, a device layer formed using an ink containing the doped metal nanoparticles will preferably be a doped device layer. Dopants, in accordance with further embodiments of the invention, are introduced in an ink formulation along with the metal nanoparticles and/or are introduced into a layer of ink before and/or after curing, to form doped a device layer, as explained in detail below.

Now referring toFIG. 1B, after the composite material is formed, then themetal nanoparticles103 are isolated from thecomposite material107. Themetal nanoparticles103 are preferably isolated from thecomposite material107 using an etchant medium to release themetal nanoparticles103 from theoxide matrix105.

After themetal nanoparticles103 are isolated from thecomposite material107, then themetal nanoparticles103 are preferably dispersed into asolvent medium109, such as illustrated inFIG. 1C. Thesolvent medium109 preferably includes one or more organic ink solvents. Suitable organic ink solvents include, but are not limited to, saturated, unsaturated, aromatic and halogenated hydrocarbons, ethers, polyethers, esters, amines, amides, alcohols, glycols, thiols, lactones, phosphates, nitriles, silanes, silicones, sulfoxides, fatty acids, germanes, ketones, terpenes, terpineols. More specific examples of suitable organic ink solvents include Mineral Spirits, toluene, xylene, mesitylene, tert-butyltoluene, pyridine, cyclohexylbenzene, tetralin, 3-octanol, 2-ethylhexanol, alpha-terpineol, dyhydroterpineol, cyclohexanone, ethyllactate, cyclomethicones, propylenglycolmonoethylether, diglyme and combinations thereof, to name a few. Futher details of Nanoparticle inks and method for making the same are described in the U.S. patent application Ser. No. 10/215,952, filed Aug. 9, 2002, and entitled “NANOPARTICLE SYNTHESIS AND FORMATION OF INKS THEREFROM”, the contents of which are hereby incorporated by reference.

Still referring toFIG. 1C, anink111, in accordance with further embodiments of the invention, comprises one or more additives such as surfactants and/or wetting agents. Surfactants include, but are not limited to, amines, amine oxides, ethers, quaternary ammonium salts, betaines, sulfobetaines, polyethers, polyglycols, polyethers, polymers, organic esters, alcohols, phosphines, phosphates, carboxylic acids, carboxylates, thiols, sulfonic acids, sulfonates, sulfates, ketones, silicones and combination thereof. More specific examples of surfactants include, but are not limited to, methyl laureate, methyl oleate, dimethyl succinate, propylenglycol, diglyme, hexadecylamine, ethyl dimethyl amine oxide, tetraoctyl ammonium bromide, poly n-vinyl pyrrolidone, octanol, tributyl phosphine, tributyl phosphate, trioctyl phosphine oxide, hexadecyl thiol, dodecyclbenzene sulfonate, diisobutyl ketone and dodecylhexacyclomethicone.

In yet further embodiments of the invention, an etchant medium (FIG. 1B) comprises a wetting agent such as a fluorinated surfactant and/or a fluorinated hydrocarbon, either alone or in combination with one or more of the aforementioned surfactants. Specific examples of wetting agents include, but are not limited to, perfluorohexanoic acid, perflourodecane, perfluoromethylvinyl ether and hexafluoropropylene oxide. It should also be noted that surfactants and/or wetting agents, such as those described above, can be included in the etchant medium to help solvate or solubilize the nanoparticles in an aqueous or organic solvent medium as themetal nanoparticles103 are being released from thecomposite material107.

Referring now toFIG. 1D, in accordance with yet further embodiments of the invention, anink121 is formulated using one or more of the silicon-based or germanium-basedmolecular precursors113, either neat or along with a suitablesolvent medium119. As, mentioned previously theink121 can be formulated with any number of different surfactants and/or wetting agents suitable for the application at hand. Themolecular precursors113, in accordance with the embodiments of the invention comprises one or more dopant elements, such as arsenic, phosphorus and/or boron, which can be incorporated into a device layer formed therefrom. A preferred use of theink121, is to deposit theink121 over a silicon seed layer formed on a suitable substrate structure, such as described in detail below.

Now referring toFIG. 1E, in accordance with further embodiments of the invention, anink131 comprises doped orundoped metal nanoparticles103 and a doped or undopedmolecular precursor113, such as described above. Theink131 can also include asolvent medium119. However, it will be clear to one skilled in the art that where themolecular precursor113 is a liquid, themolecular precursor113 can function as a solvent for themetal nanoparticles103 in the formulation of theink131. Theink131, in still further embodiments of the invention, comprises one or more surfactants, wetting agents and/or one or more dopant sources, such as previously described.

Now generally referring toFIGS. 1C–E,inks111,121 and131, in accordance with the embodiments of the invention, are formulated with any number of different additives, including a crystallization promoter. Crystallization promoters include organometallic compounds and/or metal nanoparticles of Ni, Au, Al and Fe that are dispersed or dissolved in a suitable solvent medium along with a bulk nanoparticle source.Inks111,121 and131, in addition to crystallization promoters, can also include any number of surfactants and/or wetting agents, as explained previously.

FIG. 2A is a block diagram200 outlining the step for making metal nanoparticles, formulating inks and forming device layers therefrom, in accordance with the embodiments of the present invention. In thestep201, a metal oxide precursor is treated to form a composite material comprising nanoparticles of the metal and a metal oxide matrix. Generally, forming the composite material comprises heating the metal oxide precursor, however, other methods are contemplated, including ion implantation methods, either alone or in combination with heating.

In the case where the metal oxide precursor is silicon monoxide, a composite material is formed by heating the silicon monoxide to temperatures of 600 degrees Celsius or higher for approximately one minute or more, thereby forming silicon nanoparticles embedded in a matrix of silicon oxides (such as silicon monoxide and silicon dioxide).

After the composite material is formed in thestep201, then in thestep203 the metal nanoparticles are isolated from the composite material. Referring toFIG. 2B, the metal nanoparticles are preferably isolated from the composite material by treating the composite material with an etchant medium in thestep211 to release the metal nanoparticles from the composite material, wherein the etchant medium preferentially etches (i.e. at a faster rate) the metal oxide matrix relative to the metal nanoparticles embedded therein. The etchant medium preferably comprises a hydrogen fluoride source, which is an inorganic hydrogen fluoride source (such as NH₄F, HF, KHF₂and KF or a combination thereof). In further embodiments of the invention, the hydrogen fluoride source is an organo-ammonium fluoride (such as pyridine:HF or any other secondary or tertiary amine:HF material).

Still referring toFIG. 2B, isolating the metal nanoparticles can further include the use of any number of extraction methods and techniques to remove or separate the metal nanoparticles from the etchant medium. For example, when the etchant medium is aqueous, isolating metal nanoparticles can further comprise interfacing the aqueous etchant medium with an organic extraction medium to extract the metal nanoparticles from the aqueous etchant medium after or while the metal nanoparticles are being released from the oxide matrix. In some applications it is advantageous to treat the metal nanoparticles with a surface modifier in the etchant medium to further facilitate the extraction process.

In accordance with still further embodiments of the invention, the etchant medium comprises a bistable phase medium. Bistable phase media, refer to herein as media with two or more constituents, selected from water, organic solvents, fluorinated organic solvents and surfactants which are capable of forming single and multiple phases at different temperatures.

Fluorous-phase media, for example, which generally comprise a mixture of a fluorinated solvent and another organic solvent can be used as an etchant medium, wherein the Fluorous-phase media are single phase at a first temperature and separated to a biphase media at a second, generally lower temperature. Accordingly, the composite material comprising the metal nanoparticles can be etched in such a bistable phase medium with the medium in the single phase state and then after the etching process is complete, the bistable phase medium can be cooled to form two or more separated phases, wherein the nanoparticles have a preferred affinity, or solubility, in one or more of the separated phases.

Again referring toFIG. 2A, after the metal nanoparticles are isolated using any number of etching and/or extraction/separation techniques in thestep203, in thestep205 the metal nanoparticles are used to form a nanoparticle ink. As illustrated inFIG. 2C, in order to formulate a metal nanoparticle ink, the metal nanoparticles can be treated with any number of surfactants and/or surface modifiers in thestep215 before dispersing surface modified metal nanoparticles into a suitable solvent medium in thestep217. Alternatively, the solvent medium comprises a surface modifier and/or wetting agent and the metal nanoparticles are dispensed directly into the solvent medium in thestep217. In accordance with the embodiments of the invention, the metal nanoparticles can be treated with a hydride source, such as lithium aluminum hydride, lithium borohydride, or other suitable hydride source, to form hydrogen capped metal nanoparticles. Alternatively, the metal nanoparticles isolated in thestep203 are converted to hydrogen capped metal nanoparticles by the etchant medium used. It should be noted that the nanoparticles of the present invention can also be purified and/or washed any number of times prior to dispersing the metal nanoparticles into the solvent medium. Once the metal nanoparticles are formulated into a nanoparticle ink in thestep205, in thestep207 the ink is deposited onto a suitable substrate structure which can include substrate materials such as, but not limited to, silicon, metal, quartz, glass, polymeric substrate materials and combinations thereof. The nanoparticle ink is deposited using any suitable deposition or coating technique, including but not limited to ink-jet printing, slide-bar coating, screen printing, spin coating, extrusion coating, meniscus coating, dip coating and spray coating. The layer of the nanoparticle ink is deposited in thestep207 is patterned or unpatterned.

Referring now toFIG. 2D, in accordance with the embodiments of the invention, a layer of nanoparticle ink is deposited as a continuous, or patterned layer, in thestep219. After the layer of ink is deposited as a continuous or patterned layer in thestep219, then in thestep221, the continuous, or patterned, layer is patterned, or further patterned, using liquid embossing techniques. Methods for forming patterned device layers using liquid embossing techniques are described in U.S. patent application Ser. No. 09/525,734, entitled “FABRICATION OF FINELY FEATURED DEVICE BY LIQUID EMBOSSING” and in U.S. patent application Ser. No. 09/519,722, entitled “METHOD FOR MANUFACTURING ELECTRONIC AND ELECTRO MECHANICAL ELEMENTS AND DEVICES BY THIN FILM DEPOSITION AND IMAGING”, the contents of which are both hereby incorporated by reference.

Briefly,FIGS. 3A–C illustrate the embossing technique, in accordance with the embodiments of the invention, for forming one or more patterned device layers from a nanoparticle ink oversubstrate structure300. Thesubstrate structure300 comprises any suitable substrate materials or partial device structures including conductive device layers, a dielectric device layer or combinations thereof (not shown).

Referring toFIG. 3A, in accordance with a preferred method of the invention thesubstrate structure300 is coated with a thin film of nanoparticle ink, generally referred to herein asink305. Thesubstrate300 is coated with the thin film ofink305 using any suitable coating technique such as previously mentioned. Anelastomeric stamp310 having a pattern of projecting or protrudingfeatures315 and recessedfeatures320 is lowered until the projectingfeatures315 make contact withsubstrate structure300, thereby displacingink305 at the regions of contact. The area dimensions of projectingfeatures315 are constrained by the need for these features to push aside theliquid ink305 and either make contact withsubstrate structure300 or at least displace enough liquid to facilitate its convenient subsequent removal. The maximum areas offeatures315 depend greatly on the viscosity of theink305, the thickness of the film deposited, and the material(s) used to make thestamp310.

With thestamp310 againstsubstrate structure300 as shown inFIG. 3B, the patternedfilm305′ may be partially or completely cured. In addition to patterning theliquid ink305 through displacement of theliquid ink305 away from the protruding features315 of thestamp310 and into the recessed features320 of thestamp310, thestamp310 also simultaneously facilities curing or partial curing of the patternedlayer305′ by absorption of solvent from theliquid ink305. Curing, or partial curing, of the patternedlayer305′ by absorption of solvent, helps to form a stable pattern with a high degree of feature definition. It is believed that the stamp material(s), the stamp design(s), the ink material(s) and ink formulation(s) can be judiciously selected to control the rate of solvent absorption. Materials and methods for controlling solvent absorption by a stamp during liquid embossing are further described in the U.S. patent application Ser. No. 10/288,357, filed Nov. 4, 2002, and entitled “CONTROLLED PRINT METHODS”, the contents of which are hereby incorporated by reference.

In addition, curing or partial curing in the step223 (FIG. 2D) of the patternedfilm305′ can be accomplished with thestamp310 in contact with thesubstrate structure300 and/or with thestamp310 removed from thesubstrate structure300, as shown inFIG. 3C. The preferred method or methods of curing the patternedfilm305′ is dictated primarily by the nature of theliquid ink305. Curing method, in accordance with the present invention include, but are not limited to, heating, evaporating a solvent, UV exposure, laser annealing and any combination thereof.

It is found that even if the patterned liquid305′ is not cured whilestamp310 is in contact withsubstrate300, it will tend nonetheless to retain the patterned features325 whenstamp310 is removed form thesubstrate structure300 so long as the thickness of theliquid film305 is sufficiently small. That is, there will be no detectable flow of liquid ink back into areas displaced by the projecting regions ofstamp310, probably due to the absolute height of patternedliquid layer305′ and this is believed to be facilitated by the ability of the stamp to absorb solvent form the ink during the embossing process.

Again referring toFIG. 2D, a device layer, in accordance with an alternative embodiment of the present invention is formed by depositing a continuous layer of nanoparticle ink in thestep219. After depositing the continuous layer of nanoparticle ink in thestep219, then in thestep225 the continuous layer is cured using one or more of the curing methods described previously, to form a solid phase layer. After curing the layer of ink in thestep225 to form the solid phase layer, then in thestep227 the solid phase layer is patterned using any suitable technique for patterning solid phase layers including, but not limited to, lithography, laser ablation and nanoimprint-lithography. By forming multiple layers using the method described above, either alone, or in combination with other device fabrication processes, such as lithographic processes and/or vapor deposition processes, micro devices can be fabricated.

Still referring toFIG. 2D, in thestep219, a patterned or unpatterned layer of ink is deposited onto a substrate structure that comprises a patterned or unpatterned metal layer. The metal layer preferably acts as a crystallization promoter during curing of annealing of a layer of nanoparticle ink. The metal layer, in accordance with the embodiments of the invention, comprises Ni, Au, Al and Fe or a combination thereof, and can be formed using any suitable technique, including, but not limited to, vapor deposition of a molecular precursor, electroless plating and sputtering techniques.

Now referring toFIG. 2A, after a patterned or unpatterned layer of ink is cured to form a cured device layer in thestep207, then in thestep209 the cured device layer can be further treated. In accordance with the embodiments of the present invention, the cured device layer is further treated in thestep211 by doping the layer using ion implantation or depositing a layer of material comprising a dopant over the cured device layer and annealing. Alternatively, or in addition to doping the layer in thestep211, additional patterned, unpatterned, doped and doped layers can be subsequently formed over the cured device layer.

Referring now toFIG. 4A, in accordance with an alternative embodiment of the present invention, in the step401 a silicon seed layer is formed on a suitable substrate structure. After the seed layer is formed on the substrate structure in thestep401, then in the step403 a silicon or germanium-based device layer is formed over the seed layer. The silicon and/or germanium-based device layer is preferably formed by depositing a patterned or unpatterned layer of ink comprising a silicon-based and/or germanium-based molecular precursor, such as illustrated inFIG. 1D, and curing the layer of ink. Alternatively, a device layer is formed by depositing a silicon-based and/or germanium-based molecular precursor over the seed layer using chemical or physical vapor deposition techniques. In yet further embodiments of the invention, forming a device layer comprises depositing a patterned or unpatterned layer of ink comprising metal nanoparticles over a seed layer using any suitable deposition coating technique, such as described above.

Now referring toFIG. 4B in accordance with a preferred embodiment of the invention, a seed layer is formed in thestep401, using a nanoparticle ink comprising silicon, germanium or silicon and germanium nanoparticles that are formed by disproportionation of a silicon monoxide precursor, a germanium monoxide precursor or a combination thereof, such as described previously. The seed layer can be formed by depositing a thin patterned or unpatterned layer of the nanoparticle ink onto the substrate structure in thestep406 and then in thestep408, curing the thin layer of nanoparticles, using any number suitable curing techniques described previously.

In accordance with the embodiments of the present invention, patterned, unpatterned, doped and undoped device layers are formed using nanoparticle inks to fabricate a number of different micro-devices, such as Thin-Film Transistors. Printing techniques for the fabrication of micro-devices, such as Thin Film Transistors are further described in U.S. patent application Ser. No. 10/251,077, filed Sep. 20, 2002, and entitled “FABRICATION OF MICRO-ELECTRONIC DEVICES”, the contents of which are hereby incorporated by reference.

The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention. As such, references, herein, to specific embodiments and details thereof are not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications can be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention.

Claims (19)

1. A method of fabricating a device layer comprising:

a. depositing a layer of nanoparticle ink onto a substrate structure; and

b. annealing the nanoparticle ink, wherein nanoparticles from the nanoparticle ink fuse together and wherein the nanoparticles comprise nanoparticles formed by treating a metal monoxide to form a composite material comprising a metal oxide matrix and the nanoparticles embedded therein and isolating the nanoparticles from the composite material.

2. The method ofclaim 1, wherein the nanoparticle ink comprises one or more organic solvents.

3. The method ofclaim 1, wherein the nanoparticle ink comprises a molecular precursor.

4. The method ofclaim 1, wherein the device layer is a patterned device layer.

5. The method ofclaim 4, wherein the patterned device layer is formed by at least one method selected from the group consisting of ink-jet printing, screen printing, slide-bar coating, spin coating, extrusion coating, meniscus coating, dip coating and spray coating.

6. The method ofclaim 1, wherein the nanoparticle ink comprises a dopant and wherein the device layer is a doped device layer.

7. The method ofclaim 6, wherein the dopant is incorporated into the nanoparticles.

8. The method ofclaim 1, wherein the nanoparticles comprise silicon and the nanoparticles form a seed layer and wherein fabricating the device layer further comprises decomposing a molecular silicon precursor onto the seed layer.

9. The method ofclaim 8, wherein molecular silicon precursor is decomposed onto the seed layer by vapor depositing the molecular silicon precursor on the seed layer at an elevated temperature.

10. The method ofclaim 1, wherein the nanoparticles comprise silicon and the nanoparticles form a seed layer and wherein fabricating the device layer further comprises decomposing a molecular germanium precursor onto the seed layer.

11. The method ofclaim 10, wherein the molecular germanium precursor is decomposed onto the seed layer by vapor depositing the molecular germanium precursor on the seed layer at an elevated temperature.

12. The method ofclaim 1, wherein the nanoparticles comprise silicon and the nanoparticles form a seed layer and wherein fabricating the device layer further comprises depositing a as second layer of a nanoparticle ink onto the seed layer.

13. The method ofclaim 1, wherein the device layer is a device layer in a thin-film-transistor.

14. The method ofclaim 1, further comprising doping the layer with a dopant.

15. The method ofclaim 14, wherein doping the layer comprises implanting a dopant using ion implantation.

16. The method ofclaim 14, wherein doping the layer comprises depositing a dopant material comprising a dopant over the layer and annealing the layer and the doping material to a temperature sufficient to diffuse the dopant into the layer.

17. The method ofclaim 1, wherein the layer of nanoparticle ink is deposited onto the substrate structure using a method selected from the group consisting of group consisting of ink-jet printing, screen printing, slide-bar coating, spin coating, extrusion coating, meniscus coating, dip coating and spray coating.

18. The method ofclaim 1, wherein the substrate structure comprises a layer of metal and wherein the layer of nanoparticle ink is deposited on the metal layer.

19. The method ofclaim 18, wherein the metal layer comprises a metal selected from the group consisting of Ni, Au, Al and Fe.

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